1. Field of the Invention
The present invention relates to a magnetic field-applied fabrication method for a semiconductor single crystal and an apparatus therefor, and in particular to a fabrication method which is possible to pull heavy semiconductor single crystal without dislocation even though the diameter of the contracted portion of the semiconductor single crystal is large.
2. Description of the Prior Art
The magnetic field-applied Czochralski crystal growth method (hereinafter called the MCZ method) is a method by which silicon single crystals are grown by the Czochralski method (hereinafter called the CZ method) while a magnetic field is applied to the melt by magnets surrounding a semiconductor single crystal fabrication apparatus to increase the dynamic viscosity coefficient of the melt. As the convection of the melt is inhibited by the action of the magnetic field, the temperature fluctuation near the melt surface is reduced, and thus it is possible to grow silicon single crystals stably. Moreover, as the reaction between melt and quartz crucible (SiO.sub.2) is inhibited or promoted, it is an effective method for controlling the oxygen concentration of the silicon single crystals.
The pulling of silicon single crystals by the MCZ method like that of the CZ method, includes immersing seed crystals mounted on seed chucks in the melt of a polycrystal silicon, followed by pulling the seed chucks and then growing the silicon single crystals. As dislocations occur in the seed crystal due to the heat impact imparted thereto during the dipping of it in the melt, the silicon single crystal is first grown thinner and longer in the contracting step to prevent the dislocation, then the diameter of the silicon single crystal is enlarged to a predetermined size in the shoulder-forming step, and finally the silicon single crystal is delivered to the body-forming step. The magnetic field intensity during each steps is maintained at a predetermined value.
However, in the fabrication of silicon single crystal by the MCZ method, the convection of the melt is inhibited by the application of the magnetic field, resulting in a reduction of the fluctuation of the temperature near the melt surface. This stabilize the solid-liquid interface, and thus the dislocation in the seed crystals can not be eliminated in the right and left directions and thus remains in the interior of the silicon single crystal. Accordingly, in order to completely eliminate any dislocation, when the MCZ method is used for pulling silicon single crystals, the diameter of the contracted portion must be further contracted until the dislocation is eliminated. In the fabrication of a silicon single crystal by the CZ method, the weight of the pulled silicon single crystal is limited by the diameter of the contracted portion. If the weight exceeds the limit, the contracted portion breaks, and there is the danger that the single crystal may drop. The possibility of the single crystal dropping is higher when using the MCZ method than when using the CZ method. Moreover, with the enlargement of silicon single crystals in recent years, the weight thereof increases, and thus it is more difficult to pull large-diameter silicon crystals by the MCZ method.